Combined cycle power systems and cogeneration facilities utilize gas turbines to generate power. These gas turbines typically generate high temperature exhaust gases that are conveyed into a heat recovery steam generator (HRSG) that produces steam. The steam may be used to drive a steam turbine to generate more power and/or to provide steam for use in other processes.
Operating power systems at maximum efficiency is a high priority for any generation facility. Factors including load conditions, equipment degradation, and ambient conditions may cause the generation unit to operate under less than optimal conditions. Supercharging (causing the inlet pressure to exceed the ambient pressure) turbine systems as a way to increase the capacity of gas-turbine is known. Supercharged turbine systems typically include a variable speed supercharging fan located at the gas turbine inlet that is driven by steam energy derived from converting exhaust waste heat into steam. The supercharging fan is used to increase the air mass flow rate into the gas turbine so that the gas turbine shaft horsepower can be augmented.
Additional high priorities for operators of generation facilities are maintenance costs and availability. One component of maintenance costs is equipment life. There are many factors that influence equipment life, among them are the type of fuel used, the operating hours at base load, the operating hours at peak load, and water steam injection into the compressor airflow. These factors influence the life of hot gas path parts. Increased temperatures in the turbine may have an impact on the lifetime of the components positioned along the hot gas path and elsewhere. Typically, operations above base load will reduce the lifetime of the hot gas path components while operations below base load generally will extend component lifetime. Under some conditions an operator may be willing to sacrifice efficiency for extended life of hot gas path parts in order to lessen maintenance costs. However, conventional combined cycle systems do not provide an adequate level of control of hot gas path parts life.